1. Field of the Invention
The invention relates to a process for the arylation of olefins by reaction of aromatic diazonium salts with olefins in the presence of a palladium catalyst.
2. Brief Description of the Prior Art
Arylolefins play an important role both as active compounds or intermediates for active compounds in light stabilizers and pharmaceuticals and also in the preparation of dyes. The palladium-catalysed reaction of diazonium salts with olefins is known, for example, from R. F. Heck, Palladium Reagents in Organic Synthesis, Academic Press, 1985, p. 287-290. EP-A 508 264, too, describes a process which exploits this reaction for the synthesis of arylolefins. However, the disadvantage of this process is the fact that substituted anilines are firstly converted into the corresponding diazonium salts and the reaction with olefins is only carried out subsequently with the addition of palladium compounds. On an industrial scale, this procedure has the disadvantage that large amounts of diazonium salts are present in the intervening period and these pose a considerable safety risk and also, owing to their sparing solubility, frequently result in process engineering problems.
The process of EP-A 606 057, which requires isolated diazonium salts as starting material, also has the above-mentioned disadvantages.
EP-A 553 668 describes a process for preparing arylacrylic acid derivatives in which substituted anilines are firstly diazotized and the diazonium salts are subsequently, without intermediate isolation, reacted further to form arylacrylic acid derivatives by use of carboxylic acids as solvent. However, this process does not prevent an accumulation of diazonium salts either.
There was therefore a need to develop a process which, starting from substituted or unsubstituted aminoaryl compounds, allows the palladium-catalysed preparation of arylolefins, with the diazonium salt formed as an intermediate being reacted further in situ.